The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also correspond to implementations of the claimed technology.
In a wireless network, a wireless device may be connected to an access point providing wireless data service. The wireless device exchanges vast information with the access point and other wireless devices connected over the wireless network. A lot of power is consumed by the wireless device during active transmission and reception of the information.
In order to make efficient utilization of power, the wireless device uses power saving techniques. Conventional power saving techniques includes legacy power save method, Unscheduled Automatic Power Save Delivery (U-APSD) method, Spatial Multiplexing power save method (SMPS), and Very High Throughput (VHT) Transmission Opportunity (TXOP) power save method.
In legacy power saving method, all the wireless devices announce their power save state by setting a power management bit. The power management bit is set in uplink frames having a positive acknowledgement. Upon receiving a frame with the power management bit being set, the access point starts buffering frames directed to the wireless device. Further, the access point announces a status of the buffered frame in Traffic Indication Map (TIM) field of a beacon frame.
Using the TIM field of the beacon frame, the wireless device discovers about buffered frames being present at the access point. Successively, the wireless device polls for the buffered frames present at the access point. The wireless device polls by transmitting PS-Poll frame when more data bit is set in received downlink Data frames or Management frames. The access point delivers the buffered frames upon receiving the PS-Poll frames from the wireless device. The wireless device can enter into a sleep state upon receiving the buffered frame with a more data field set to zero.
Also, upon receiving beacon frame with TIM element indicating absence of buffered data at the access point, the wireless device enters into the sleep mode. The wireless device remains in the sleep mode until a specified time period. After the specified time period lapses, the wireless device wakes up and operate actively to receive the beacon frames. The wireless device operates further based on data present in the beacon frames.
In one case stations may be connected to an Access Point (AP). In one exemplary case, five stations may be served by a Very High Throughput (VHT) Access point (AP). Further, the number of stations connected to the VHT Access Point may be lesser than or more than five in other implementations. The group may comprise Very High Throughput (VHT) Transmission Opportunity (TXOP) power saving stations (STA's) VHT STA1 and VHT STA2 and non-VHT UAPSD/Legacy power saving stations non-VHT STA3, non-VHT STA4, and non-VHT STA5.
In the FIG. 1, a data flow sequence diagram for stations using the legacy power saving method is illustrated. The AP transmits a beacon frame to connected stations. The beacon frame indicates presence of data at the AP, destined for different stations. Using the beacon frame, non-VHT station STA5 determines absence of any buffered frame for itself at the AP. Thus, the non-VHT station STA5 enters into a sleep state, immediately after reading the beacon frame.
Non-VHT stations STA3 and STA4 each transmits a poll/trigger and waits for receiving their buffered frames from the AP. The non-VHT stations STA3 and STA4 are later served by the AP by sending their buffered data. The buffered data sent to the non-VHT stations STA3 and STA4 are shown as non-VHT Physical Layer Protocol Data Unit (PPDU) (3) and non-VHT PPDU (4) respectively. Successively, the non-VHT stations STA3 and STA4 send to the AP, acknowledgements for received buffered data. Thus, the non-VHT stations STA3 and STA4 remain in an active state till receiving the buffered data.
The VHT stations STA1 and STA2 remain in an active state to receive their buffered data present at the AP. The VHT station STA1 receives the buffered data VHT Multi User (MU)-PPDU (1, 2) and immediately enters into sleep state after sending a Block Acknowledgement (BA). The VHT station STA2 receives the buffered data VHT MU-PPDU (1, 2) and later receives VHT SU-PPDU (2). Thus, the VHT stations STA1 and STA2 stayed in an active state. Therefore, power wastage occurs at the VHT station STA2 and the non-VHT stations STA3 and STA4 because of random transmission of data by the AP and thus continuous presence of the stations in active state.
The Unscheduled Automatic Power Save Delivery (U-APSD) power saving method operates only for delivery of downlink Quality of Service (QoS) data frames. The U-APSD power saving method does not operate on non-QoS frames and management frames. In the U-APSD power saving method, a power saving station does not poll to fetch buffered frames present at an AP. Instead, uplink QoS-data or a QoS-Null data frame acts as a trigger for delivery of downlink frames. Thus, in the U-APSD power saving method, an overhead to PS-Poll for all the buffered frames is eliminated.
In the FIG. 2, a data flow sequence diagram for stations using the Unscheduled Automatic Power Save Delivery (U-APSD) power saving method is illustrated. The AP transmits a beacon frame to connected stations. The beacon frame indicates presence of buffered data destined for the stations connected to the AP. Buffered data VHT MU-PPDU (1, 2) is received by VHT stations STA1 and STA2. VHT station STA2 also receives buffered data VHT SU-PPDU (2). Post receiving the buffered data, the VHT stations STA1 and STA2 may enter into a sleep state.
In one case, a partial AID associated with the VHT SU-PPDU may not match with a partial AID of the VHT station STA1. Thus, the VHT station STA1 may enter into a sleep state. In another case, a group identity (ID) associated with the VHT MU-PPDU may not match with a group ID of a group comprising the VHT stations STA1 and STA2. Thus, the VHT stations STA1 and STA2 may enter into a sleep state. In yet another case, a group ID associated with the VHT MU-PPDU may match with a group ID of the group comprising the VHT stations STA1 and STA2. Further, a Number of Spatial Streams (NSTS) corresponding to the stations STA1 and STA2 may be zero. Thus, the stations STA1 and STA2 may enter into a sleep state.
The AP has buffered data comprising non-VHT PPDU (3), non-VHT PPDU (4), and non-VHT PPDU (5) for the non-VHT stations STA3, STA4, and STA5 respectively. FIG. 2 shows that the AP served the VHT stations at first and subsequently serves the non-VHT stations. The non-VHT stations STA3, STA4, and STA5 wait constantly for receiving the buffered data present at the AP. Thus, power wastage occurs in the UAPSD power saving method, by the non-VHT stations remaining in a waiting and active state for entire TXOP period.
Very High Throughput (VHT) Transmission Opportunity (TXOP) power saving method is an IEEE 802.11ac power saving feature. All associated stations may be divided into different groups. Every group may be assigned with a unique group identity. The TXOP power saving method may use a MU-PPDU comprising a specific group ID.#
In one case, a VHT AP may announce a group ID during initialization. The group ID associated with the MU-PPDU may be matched with identities of stations connected to the AP. The stations, whose identities do not match with the group ID, may enter into a sleep state during the TXOP period.#Successively, the VHT AP may serve remaining stations whose identities match with the group ID. #
The VHT AP may allow associated VHT TXOP power saving stations to enter into a sleep state by setting a TXOP_PS_NOT_ALLOWED TX-VECTOR parameter to zero. The TXOP_PS_NOT_ALLOWED TX-VECTOR parameter may be set to zero in a VHT SU-PPDU or in a VHT MU-PPDU. But, non-VHT stations cannot change their power save state in VHT TXOP power save mode, thus wasting power. Thus, a method of saving power in non-VHT stations is much desired.